Studies will be done to determine the mechanisms of invasion of the rodent liver by the sporozoite of the rodent malaria parasite, Plasmodium berghei. Attempts will be made to study this process morphologically at the fine structural level both in vivo and in vitro. Host cells being invaded, and the route of invasion will be examined by labelling of sporozoites with immunochemical markers. Studies will be done at the biochemical level to characterize the nature of proteins which may be involved in this invasive process, and the physiology of secretion of this material by the sporozoite. Attempts will be made to identify receptor sites on the surface of the sporozoite, which might aid it in recognition and attachment to the appropriate host liver cell. It is hoped that these studies may lead to better ways to interfere with this process, either by immunological or pharmacological means.